The present invention relates to systems for assembling, in particular by welding, structures made up of elements of pressed sheet metal, such as motor-vehicle bodies or subassemblies thereof.
In particular, the invention regards an assembly system designed to operate automatically on a plurality of different types of structures to be assembled, for example, on bodies of different models, of the type comprising:                a station for assembly, in particular by welding;        conveying means for carrying at least part of the structures to be assembled to the assembly station and for carrying the assembled structures out of the assembly station; and        a plurality of pairs of side frames provided with position-referencing and clamping means for positioning and clamping the structures to be assembled, the referencing and clamping means provided on the side frames of each pair being adapted to the configuration of a corresponding type of structure to be assembled,        
in which the pairs of side frames are movable on guide means for enabling replacement, according to the type of structure to be assembled, of the pair of side frames that are present in the assembly station,
in which each pair of side frames is carried by a respective basic structure that is movable through the assembly station so as to form with the two frames a unitary movable referencing and clamping module, said side frames being mounted on the respective basic structure in such a way that they can be displaced transversely with respect to a longitudinal direction of said basic structure, between an open condition where the side frames are set at a greater distance apart, in which a structure to be assembled can be received between said frames or an assembled structure can come out of the space comprised between said frames, and a closed condition, in which the two frames are rigidly connected together and their referencing and clamping means can engage the structure to be assembled.
The known systems of the type referred to above present the drawback of having a relatively complex structure and of requiring operations that are relatively complicated and expensive in terms of time for replacement of the pair of side frames that are in the operative position inside the assembly station.